Electroanalytical Performance of (SiPy+Cl−/CuTsPc)5 LbL Film for Detecting Promethazine Hydrochloride

A (SiPy⁺Cl^?/CuTsPc)₅ layer‐by‐layer film was employed for the electroanalytical determination of promethazine hydrochloride in BR buffer pH 5.0 with peaks at 0.48 and 0.79 V. After optimisation of the square‐wave parameters (f=100 s^?1, a=40 mV and ΔE_s=2 mV), the peak at 0.79 V was used for quantification and a detection limit of 8.71×10^?9 mol L^?1 and a quantification limit of 9.31×10^?8 were calculated. The applicability of this procedure was tested on commercial formulations of promethazine hydrochloride by observing the stability, specificity, recovery and precision of the procedure in complex samples, without any preliminary treatment.     

Electrochemistry and Electrocatalysis of a Nafion/Nano‐CaCO3/Hb Film Modified Carbon Ionic Liquid Electrode Using BMIMPF6 as Binder

In this paper a room temperature ionic liquid 1‐butyl‐3‐methylimidazolium hexafluorophosphate (BMIMPF₆) was used as binder for the construction of carbon ionic liquid electrode (CILE) and a new electrochemical biosensor was developed for determination of H₂O₂ by immobilization of hemoglobin (Hb) in the composite film of Nafion/nano‐CaCO₃ on the surface of CILE. The Hb modified electrode showed a pair of well‐defined, quasi‐reversible redox peaks with E_pa and E_pc as ?0.265 V and ?0.470 V (vs. SCE). The formal potential (E°′) was got by the midpoint of E_pa and E_pc as ?0.368 V, which was the characteristic of Hb Fe(III)/Fe(II) redox couples. The peak to peak separation was 205 mV in pH 7.0 Britton–Robinson (B–R) buffer solution at the scan rate of 100 mV/s. The direct electrochemistry of Hb in the film was carefully investigated and the electrochemical parameters of Hb on the modified electrode were calculated as α=0.487 and k_s=0.128 s^?1. The Nafion/nano‐CaCO₃/Hb film electrode showed good electrocatalysis to the reduction of H₂O₂ in the linear range from 8.0 to 240.0 μmol/L and the detection limit as 5.0 μmol/L (3σ). The apparent Michaelis–Menten constant (K_M^app) was estimated to be 65.7 μmol/L. UV‐vis absorption spectroscopy and FT‐IR spectroscopy showed that Hb in the Nafion/nano‐CaCO₃ composite film could retain its native structure.     

Determination of Zirconium and Vanadium in Natural Waters by Adsorptive Stripping Voltammetry in the Presence of Cupferron,Oxalic Acid and 1,3‐Diphenylguanidine

A sequential AdSV method based on the accumulation of Zr(IV) and V(V) as cupferron‐oxalic acid‐1,3‐diphenylguanidine (COD) complexes at the HMDE was used to determine traces of these metals in samples with different ionic strengths. DP mode, E_ads ?0.6 and ?0.2 V (vs. Ag/AgCl, 3 mol L^?1 KCl), t_ads 400 and 20 s and 10 and 60 mV s^?1 scan rates were used for Zr(IV) and V(V), respectively. E_peak were ?0.95 (Zr(IV)‐COD) and ?0.65 V(V(V)‐COD). The methodology was applied in samples of rivers, estuaries (in Germany and Brazil) and coastal and open seawater.     

Electroanalytical Determination of N‐Nitrosamines in Aqueous Solution Using a Boron‐Doped Diamond Electrode

The electrochemical methods cyclic and square‐wave voltammetry were applied to develop an electroanalytical procedure for the determination of N‐nitrosamines (N‐nitrosopyrrolidine, N‐nitrosopiperidine and N‐nitrosodiethylamine) in aqueous solutions. Cyclic voltammetry was used to evaluate the electrochemical behaviors of N‐nitrosamines on boron‐doped diamond electrodes. It was observed an irreversible electrooxidation peak located in approximately 1.8 V (vs. Ag/AgCl) for both N‐nitrosamines. The optimal electrochemical response was obtained using the following square‐wave voltammetry parameters: f=250 Hz, E_sw=50 mV and E_s=2 mV using a Britton–Robinson buffer solution as electrolyte (pH 2). The detection and quantification limits determined for total N‐nitrosamines were 6.0×10^?8 and 2.0×10^?7 mol L^?1, respectively.     

Electroanalytical Studies on Cobalt(II) Ion‐Selective Sensor of Polymeric Membrane Electrode and Coated Graphite Electrode Based on N2O2 Salen Ligands

Poly(vinyl chloride)‐based membranes of salen ligands, 2‐((E)‐((1R,2S)‐2‐((E)‐5‐tert‐butyl‐2‐hydroxybenzylideneamino)cyclohexylimino)methyl)‐4‐tert‐butyl phenol (S₁) and 2‐((E)‐((1R,2S)‐2‐((E)‐3,5‐di‐tert‐butyl‐2‐hydroxybenzylideneamino)cyclohexylimino)methyl)‐4,6‐di‐tert‐butylphenol (S₂) were fabricated and explored as cobalt(II) selective electrodes. The performance of the polymeric membrane electrode (PME) and coated graphite electrode (CGE) were compared and it was observed that CGE showed a wide working concentration range of 1.1×10^?8 to 1.0×10^?1 mol L^?1 with a limit of detection of 7.0×10^?9 mol L^?1 exhibiting the Nernstian slope 29.6 mV/decade of activity in the pH range 3.0–9.0. It was used for the determination of cobalt(II) ions in water, soil, beer, pharmaceutical samples and medicinal plants and would be used as an indicator electrode in potentiometric titration with EDTA.     

A Hydrogen Peroxide Biosensor Based on Room Temperature Ionic Liquid Functionalized Graphene Modified Carbon Ceramic Electrode

A room temperature ionic liquid (IL) 1‐butyl‐3‐methylimidazolium hexafluorophosphate functionalized graphene (GE) was prepared and a hydrogen peroxide (H₂O₂) biosensor was fabricated by immobilizing hemoglobin (Hb) into the IL‐GE composite film. UV‐visible and Fourier transform infrared spectra of the composite film indicated that Hb retained its native structure in the film. Electrochemical investigation of the biosensor showed a pair of well‐defined, quasi‐reversible redox peaks with E_pa=?0.209 V and E_pc= ?0.302 V (vs. SCE) in pH 7.0 phosphate buffer solution at the scan rate of 100 mV/s. To the reduction of H₂O₂, the biosensor had a good linear range from 8.0×10^?7 to 1.8×10^?4 mol/L with a detection limit of 3.0×10^?7 mol/L. The apparent Michaelis‐Menten constant K^app_M was estimated to be 3.4×10^?5 mol/L.     

Electrochemical Characterization of Epigallocatechin Gallate Using Square‐Wave Voltammetry

Electrochemical oxidation of (?)‐epigallocatechin gallate (EGCG), the main monomer flavanol found in green tea, has been investigated over a wide pH range at a glassy‐carbon electrode using square‐wave voltammetry (SWV). Square‐wave voltammograms of (?)‐epigallocatechin (EGC) and gallic acid have been studied as well. The I–E profile of EGCG, i.e. the oxidation potentials and the current responses of the first and the second peak, is pH dependent. The oxidation of EGCG is a quasireversible process over the studied pH range, which was also confirmed by the non‐linear relationship between the peak currents and squre root of frequency. The best SWV responses for EGCG were obtained at pH 2.0, frequency of 100 Hz, step of 2 mV and amplitude of 50 mV. Under these conditions, linear responses for EGCG were obtained for concentrations from 1×10^?7 M to 1×10^?6 M, and calculated LOD and LOQ for the first oxidation peak were 6.59×10^?8 M and 2.19×10^?7 M, respectively. The proposed electroanalytical procedure was applied for the determination of EGCG content in green tea. Developed SWV methodology represents a potential analytical tool in determination of catechins in tea samples.     

Effect of the Peptidic Scaffold in Copper(II) Coordination and the Redox Properties of Short Histidine‐Containing Peptides

A linear decapeptide containing three His and one Asp residues and a β‐turn‐inducing dProPro unit was synthesised. A detailed potentiometric, mass spectrometric and spectroscopic study showed that at a 1:1 ratio of C_Cu/C_peptide this peptide formed a major [CuH(O_dPro?Asp)]²⁺ species (pH range 5.5–7.0), in which the Cu²⁺ ion was bound to the His and Asp residues in square‐planar or square‐pyramidal geometries. The stability constant corrected for protonated species (log K*=9.33) is almost equal to the value obtained for the parent [CuH(O?Asp)]²⁺ species (log K*_CuH(O‐Asp)=9.28), but lower than that obtained for the cyclic [CuH(C?Asp)]²⁺ complex (log K*_CuH(C‐Asp)=10.79) previously published. Thus, the replacement of the ProGly unit by the stronger β‐turn‐inducing dProPro unit did not generate a more stable copper(II) species, although the O_dPro?Asp peptide was structured in solution, as shown by circular dichroism (CD) spectroscopy. Interestingly, the calculated value of K_eff showed that this peptide behaved similarly to the O?Asp or C?Asp counterparts, depending on the pH value. The cyclic voltammetry data indicated that the most easily reducible species were [CuH(O?Asp)]²⁺ (E′⁰=262 mV versus a normal hydrogen electrode (NHE)) and [CuH(O_dPro?Asp)]²⁺ (E′⁰=294 mV versus NHE) complexes, the peptidic scaffolds of which are open. A lower value was obtained for [CuH(C?Asp)]²⁺ (E′⁰=24 mV versus NHE). A different degree of non‐reversibility was observed for the three copper(II) complexes; this could reflect a different degree of flexibility in their respective peptidic scaffolds.     

Electrochemical Interrogation and Sensor Applications of Nanostructured Polypyrroles

The polymerization of pyrrole in β‐naphthalene sulfonic acid (NSA) gave nanotubules, nanomicelles or nanosheets of polypyrrole (PPy) depending on the amount of NSA in the polymer and the temperature of the reaction. Scanning electron microscopy (SEM) measurements showed that the diameters of the nanostructured polypyrrole‐β‐naphthalene sulfonic acid (PPyNSA) composites were 150–3000 nm for the tubules, 100–150 nm for the micelles and 20 nm for the sheets. A red shift in the UV‐vis absorption spectra of PPy was observed for PPyNSA which indicates the involvement of bulky β‐naphthalene sulfonate ion in the polymerization process. The UV‐vis also showed the existence of polaron and bi‐polaron in the polymer which may be responsible for the improved solubility of PPyNSA compared to PPy. All the characteristic IR bands of polypyrrole were observed in the FTIR spectra of PPyNSA, with slight variation in the absolute values. However, the absence of N? H stretching at 3400 cm^?1 and 1450 cm^?1 usually associated with neutral polypyrrole confirms that the polymer is not in the aromatic state but in the excited polaron and bipolaron defect state. Electrochemical analysis of PPyNSA reveals two redox couples: a/a′ – partly oxidized polypyrrole‐naphthalene sulfonate radical cation/neutral polypyrrole naphthalene sulfonate; b/b′ – fully oxidized naphthalene sulfonate radical cation/partly reduced polypyrrole‐naphthalene sulfonate radical anion. The corresponding formal potentials measured at 5 mV/s, E°′_{(5 mV/s)}, are 181 mV and 291 mV, respectively. Amperometric phenol sensor constructed with PPyNSA on a glassy carbon electrode (GCE) gave a sensitivity of 3.1 mA M^?1 and a dynamic linear range of 0.65–139.5 μM. The data for the determination of phenol on the GCE/PPyNSA electrode was consistent with the electrocatalytic Michaelis‐Menten model, giving an apparent Michaelis‐Menten constant (K_M′) value of 160 μM.     

New insights on the Cd UPD on Au(111)

The Cd underpotential deposition (UPD) process on Au(111) was analyzed by means of combined electrochemical measurements and in situ scanning tunneling microscopy (STM). In the underpotential range 300?ΔE (mV) ?400, 2D Cd islands are formed on the fcc regions of the Au(111)‐(√3 × 22) reconstructed surface without lifting the reconstruction. At lower underpotentials, the 2D Cd islands grow and, simultaneously, new 2D islands nucleate and coalesce with the previous ones forming a complete condensed Cd monolayer (ML). STM images and long time polarization experiments performed at ΔE = 70 mV demonstrate the formation of an Au? Cd surface alloy. At ΔE = 10 mV, the formation of the complete Cd ML is accompanied by a significant Au? Cd surface alloying and the kinetic results reveal two different solid‐state diffusion processes. The first one, with a diffusion coefficient D₁ = 4 × 10^?17 cm² s^?1, could be ascribed to the mutual diffusion of Au and Cd atoms through a highly distorted (vacancy‐rich) Au? Cd alloy layer. The second and faster diffusion process (D₂ = 7 × 10^?16 cm² s^?1) is associated with the appearance of an additional peak in the anodic stripping curves and could be attributed to the formation of another Cd_zAu_x alloy phase. Copyright © 2008 John Wiley & Sons, Ltd.     

Simple Strategy for Selective Determination of Levamisole in Seized Cocaine and Pharmaceutical Samples Using Disposable Screen‐printed Electrodes

Levamisole is the most common adulterant found in cocaine samples and its electrochemical determination in cocaine seized samples is a challenge due to peak overlapping with cocaine. Herein, we propose a deconvolution procedure for levamisole determination in seized cocaine samples using screen‐printed carbon electrodes (SPE). Square‐wave voltammetry in 0.04 mol L^?1 Britton Robinson buffered solution (pH 8.0) was selected in combination with optimized SWV parameters (f=8 s^?1, a=10 mV and ΔE_s=1 mV) to result in the best peak resolution to apply the deconvolution procedure. Deconvoluted responses of levamisole in the presence of cocaine were similar to untreated signals of standard levamisole solutions in absence of cocaine. A linear response was obtained in the range of 20–100 μmol L^?1 (r=0.995). The results obtained for the analysis of a seized cocaine sample was statistically similar to that obtained by gas chromatography. Other adulterants found in cocaine street samples (paracetamol, glucose, phenacetin, caffeine, boric acid and lidocaine) did not affect the treated of voltammetric responses of levamisole. A pharmaceutical sample containing levamisole was also analyzed on SPEs and a recovery of 93±2 % was obtained (no deconvolution required for this sample), showing great applicability of SPEs for forensic and pharmaceutical analyses.     

Redox Properties of the Iron Complexes of Orally Active Iron Chelators CP20, CP502, CP509, and ICL670

Redox cycling of iron is a critical aspect of iron toxicity. Reduction of a low‐molecular‐weight iron(III)‐complex followed by oxidation of the iron(II)‐complex by hydrogen peroxide may yield the reactive hydroxyl radical (OH^.) or an oxoiron(IV) species (the Fenton reaction). Complexation of iron by a ligand that shifts the electrode potential of the complex to either to far below ?350 mV (dioxygen/superoxide, pH=7) or to far above +320 mV (H₂O₂/HO^., H₂O pH=7) is essential for limitting Fenton reactivity. The oral chelating agents CP20, CP502, CP509, and ICL670 effectively remove iron from patients suffering from iron overload. We measured the electrode potentials of the iron(III) complexes of these drugs by cyclic voltammetry with a mercury electrode and determined the dependence on concentration, pH, and stoichiometry. The standard electrode potentials measured are ?620 mV, ?600 mV, ?535 mV, and ?535 mV with iron bound to CP20, ICL670, CP502, and CP509, respectively, but, at lower chelator concentrations, electrode potentials are significantly higher.     

Sensitive Simultaneous Determination of o-Nitrophenol and p-Nitrophenol in Water by Surfactant-Mediated Differential Pulse Voltammetry

A simple, low-cost and sensitive electroanalytical method was developed for the simultaneous determination of p-nitrophenol and o-nitrophenol isomers in water samples at a glassy carbon electrode (CGE) in the presence of cationic surfactant. The electrochemical behavior of p-nitrophenol and o-nitrophenol was studied by cyclic voltammetry (CV) in 0.1?mol L^?1 acetate/acetic acid buffer (pH 3.70) in the presence and absence of cetylpyridinium bromide. The resolution of overlapped cathodic peaks potentials (E_pc) of isomers was successfully improved in the presence of 100.0?µmol L^?1 cetylpyridinium bromide, thus making this approach ideal for the simultaneous determination of isomers. Under the optimized conditions in 0.05?mol L^?1 HEPES buffer at pH 7.0 using differential pulse voltammetry (DPV) at a scan rate of 45?mV s^?1, pulse amplitude of 220?mV and modulation time of 10?ms, limits of detection 0.59?µmol L^?1 for p-nitrophenol and 1.14?µmol L^?1 for o-nitrophenol were obtained with linear ranges from 2.0 to 60.0?µmol L^?1 and 3.0 to 60.0?µmol L^?1, respectively. The intraday precision was assessed as relative standard deviation (%) for 20.0 and 40.0?µmol L^?1 concentrations were 4.30% and 2.41% for p-nitrophenol and 4.87% and 2.20% for o-nitrophenol, respectively. The developed method was applied for the determination of the isomers in lake water samples. The accuracy was attested by comparison with high-performance liquid chromatography with diode array detection (HPLC-DAD) as a reference analytical technique. Recovery values ranging from 90.3% to 111.8% also attested to the accuracy of method for analysis of real samples.     

Electrochemical Properties of Hydroxyphenazine-Coated Electrodes

Glassy carbon and gold electrodes were coated with 1-hydroxyphenazine, and the electrochemical properties of these electrodes were tested using them as a rotating disc electrode to reduce Ru (bipy)₃³⁺, Fe³⁺, quinoxaline, O₂, and to oxidize Eu²⁺. The fixed redox couple can be reversibly reduced and oxidized, and acts as an intermediate medium for the electron transfer. For example the Ru(bipy)₃³⁺ (E_1/2= 1010 mV vs. SCE. (saturated calomel electrode) on a glassy carbon electrode in 1M H₂SO₄) is only reduced at 50 mV, whereas the oxidation of Eu²⁺ (E_1/2= ?460 mV vs. SCE. on a Hg-electrode in 1M HCl) takes place at ? 100 mV. The heterogeneous rate constant depends on the second order reaction between the attached coating and the redox couple in solution. Depending on this rate constant, selectivity of the electrode is observed.     

Thermal,magnetic and spectral studies of metal-quinone complexes. Part II. Media effect on Coligation of Aqua Ligands

Syntheses of phthiocol complexes with Cu(II) in inert media resulted in anhydrous monomer Cu-4: [Cu(NQ)₂] and dimer Cu-5: [Cu(NQ)(NSQ)]₂, however synthesis in air generates polymeric hydrated Cu-6: [Cu(NQ)₂(H₂O)₂]_n. Media and colligation give rise to charge transfers in coordination compounds and lead to different redox ligations of 3-methyl-2-hydroxy-1,4-naphthoquinone. These redox forms are determined from quantitization of activation energies (E _a) of different pyrolytic steps in TG using the rising temperature expression of Coats and Redfern. 'Tyrosinase'-type mechanism is discussed for the redox-type ligation. Characteristic six-line EPR signals of dimeric Cu-5 lead to zero field splitting parameters D=0.01608 cm^-1and E=0.01576 cm^-1. Cu-6 shows molecular association through hydrogen bonding. Variable temperature magnetic measurement data of Cu-6 from 6 to 300 K is fitted to the polymeric expression of Bonner and Fisher model. The best fit was obtained with antiferrromagnetic exchange coupling constantJ=-2 cm^-1, g=2.2 having R=4.2·10^-4. This revised version was published online in July 2006 with corrections to the Cover Date.     

Synthesis,crystal structure,spectroscopy, and electrochemistry of a uranium complex

A uranium coordination compound with pyridine-2,6-dicarboxylic acid in deionized water has been synthesized and characterized by IR, UV, XPS, and X-ray single-crystal diffraction. The crystal belongs to the monoclinic system, space group C2/c with a?=?1.8427(4)?nm, b?=?0.6886(16)?nm, c?=?1.5442(4)?nm, α?=?90°, β?=?94.082(2)°, γ?=?90°, Z?=?4, and V?=?1.9544(8)?nm³. The structure shows an eight-coordinate uranium forming a hexagonal bi-pyramidal 3-D geometry with pyridine-2,6-dicarboxylate as building units. Fluorescent studies show several strong emissions. Cyclic voltammetric measurement of the compound reveals that uranium(VI) is reduced irreversibly at E _1/2?=?927?mV with ΔE _p?=?77?mV, E _1/2?=??289?mV with ΔE _p?=?113?mV. The electron transfer number (n) involved in reduction processes could be calculated to be approximately two and one, which corresponded to the unusual U(VI)/U(IV) and U(IV)/U(III) couples.     

Voltammetric Determination of Cocaine Using Carbon Screen Printed Electrodes Chemically Modified with Uranyl Schiff Base Films

Chemically modified screen printed electrodes (CM‐SPE) using [UO₂(4‐MeOSalen)(H₂O)] ? H₂O films were employed in the voltammetric determination of cocaine. The chemical modification was performed by dip coating electrode surfaces (carbon, gold, and platinum) with methanolic solution containing the Schiff base complex with subsequent drying step at room temperature. The optimized amount of the chemical modifier over the working electrode was found to be 2.39 µg mm^?2 (geometric area). The voltammetric measurements were carried out in 50 : 50 v/v methanol:water solution containing 0.05 mol L^?1 KCl and 0.1 mol L^?1 LiCl as a supporting electrolyte without oxygen elimination by inert gas flow. The best results were obtained with carbon electrodes. Cocaine exhibits a well defined irreversible anodic peak current (i_pa) at a potential (E_pa) of 0.85 V vs Ag/AgCl. The current is directly proportional to the drug concentration. An optimal accumulation potential (E_prec), and time (t_prec) of ?0.80 V (vs Ag/AgCl), and 120 s, respectively, were determined. The linear dependence of i_pa with square root of scan rate (υ) indicates that the mass transport at the electrode surface is controlled by diffusion. An optimized scan rate of 100 mV s^?1 was obtained for analytical purposes. A limit of detection (LOD) and limit of quantification (LOQ) in 110 and 390 µmol L^?1, respectively, with intra and inter‐day repeatability of 2.61 % and 3.77 %, respectively, were obtained. In interference studies the proposed method demonstrated high specificity for cocaine in the presence of morphine and 3,4‐methylenedioxymethanphetamine. The above results demonstrate that this method provides a fast and low cost procedure for determination of cocaine in trace levels.     

Determination of the Natural Dissolved Concentration of Zirconium in Seawater by Adsorptive Stripping Voltammetry

A voltammetric method was developed for zirconium determination as Zr(IV)‐cupferron‐oxalate‐diphenylguanidine complex based on adsorptive accumulation at the HMDE (E_peak=?0.95 V). The supporting electrolyte was a mixture of acetate/acetic acid (pH 4.6) and ammonium acetate (pH 5.7) solutions. E_ads=?0.6 V (vs. Ag/AgCl), t_ads=400 s, 10 mV s^?1 scan rate, and DP mode were the main parameters. The linear range was 0.033 to 3.3×10^?9 mol L^?1, and the LOD and LOQ (t_ads=400 s) were 0.77 and 1.6×10^?11 mol L^?1, respectively. The method was adequate for seawater samples, although not sufficiently sensitive for surface waters.     

Amperometric Sensor for Trichloroacetic Acid Based on Myoglobin/Colloidal Gold Nanoparticles Immobilized in Titania Sol–Gel Matrix

A new amperometric sensor for the determination of trichloroacetic acid (TCA) was developed based on the immobilization of myoglobin/colloidal gold nanoparticles in titania sol–gel matrix. The sensor showed a pair of well‐defined and nearly reversible cyclic voltammetric peaks for the Mb Fe(III)/Fe(II) with a formal potential (E°′) of ?335 mV and a peak‐to‐peak separation was 61 mV vs. Ag/AgCl (3.0 M KCl) at 100 mV s^?1 in 0.1 M pH 7.0 phosphate buffer solutions (PBS). The formal potential of the Mb Fe(III)/Fe(II) couple shifted linearly with the pH with a slope of ?51.3 mV/pH, indicating that an electron transfer accompanies single‐proton transportation. The sensor displayed a good electrocatalytic response toward the reduction of TCA and the catalytic mechanism was also discussed. The overpotential for the reduction of TCA was lowered by at least 0.8 V compared with that obtained at bare glassy carbon electrode. The linear range spans the concentration of TCA from 2.0×10^?6 to1.2×10^?5 M and the detection limit was 1.2×10^?7 M. In addition, the stability, repeatability and selectivity of the sensor were also evaluated.